Brief Warmth, Then a Significant Cooldown

FastCast--Wednesday, Oct. 18 to Tuesday, Oct. 24:

With a strong atmospheric river directed into British Columbia, warm southerly flow will bring mostly sunny conditions to Western Washington on Wednesday and Thursday, with highs increasing significantly to the upper 60s to low 70s. However, from Friday onward, temperatures will decline significantly, ending up below average by next week. On Friday, expect mostly cloudy skies with highs dropping to the low to mid 60s. Cloudy conditions with a chance of showers will prevail from Saturday to Monday, with highs in the upper 50s to low 60s. From Wednesday to Sunday, expect lows in the upper 40s to low 50s. On Monday, expect lows to drop to the mid 40s. By Tuesday, the chance of showers will increase, and highs will drop to the upper 40s to low 50s, with lows in the upper 30s to low 40s. These colder temperatures will continue into next week, so stay tuned for updates.

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Washington will experience a few more days of above average temperatures, before a significant cooldown will bring colder temperatures to the Pacific Northwest starting next week. Let's take a look at the forecast!

Let's start with the forecast for high temperatures from the European model, starting with Wednesday's highs.

Expect lowland and Willamette Valley highs in the upper 60s to low 70s, with similar highs in Eastern Washington. Coastal highs will reach the low to mid 60s. Notice cooler highs from Bellingham northward, as a strong atmospheric river impacts British Columbia. Clouds associated with this atmospheric river will bring cooler temperatures to Whatcom, San Juan, and Clallam Counties. 

Next, let's look at Thursday's highs, also from the European model.

On Thursday, expect lowland and Willamette Valley highs in the upper 60s to low 70s, with Eastern Washington reaching the upper 60s to mid 70s, the coast reaching the low to mid 60s, and areas under the atmospheric river (North Coast & NW Interior) reaching the low 60s.

Friday's highs will cool west of the Cascades, but remain warm to the east. The European model forecast is below.

On Friday, expect lowland highs in the upper 50s to low 60s, coastal highs in the low to mid 60s, Willamette Valley highs in the mid 60s to low 70s, and Eastern Washington's highs in the upper 60s to mid 70s. Areas along the Strait of Juan de Fuca and in the NW Interior will remain in the mid 50s to low 60s.

On Saturday, temperatures will continue to decrease in the lowlands, while remaining warm in Eastern Washington, as seen below.

On Saturday, lowland highs will decrease to the upper 50s to low 60s, with the Willamette Valley reaching the low to mid 60s, and the coast reaching the upper 50s. Eastern Washington will remain warm, with highs reaching the upper 60s to mid 70s.

Now, let's take a look at the reason for both the warm temperatures on Wednesday and Thursday and the cooler temperatures in the state's northwest corner. A potent atmospheric river is aimed directly at Southern British Columbia, barely clipping NW Washington. The European model forecast shows total rain from this atmospheric river.

Notice 0.1-0.2" of rain from Snohomish County southward in Western Washington. Most of this rain has already fallen. Areas from Everett to Bellingham could get 0.2-0.4" of rain. The atmospheric river has a very sharp cutoff on its south side. From Forks northward on the coast and north of a line from Orcas Island to Lynden will get 0.5-2.5" of rain. Parts of the Vancouver Island coast (like Tofino) will get a staggering 8-12" of rain in under 3 days, with Metro Vancouver, eastern Vancouver Island, and the Sunshine Coast getting 2.5-5".

The contrast is most notable between Bellingham and Vancouver, 45 miles as the crow flies. Bellingham will get 0.3", while Vancouver will get up to 3.5"!

We'll round out the blog by looking at the extended forecasts for Seattle and Spokane, seen on the European EPS model.

First, Seattle, seen below.

Notice warmth and above average temperatures until around Monday, then a significant change to below average conditions, with highs in the low to mid 50s and lows in the upper 30s to mid 40s.

A similar situation is seen in the forecast for Spokane, seen below.

In Spokane, highs will be warmer than Seattle (through Saturday), then cooler than Seattle (Monday onward), with lows remaining colder than Seattle. By next week, Spokane's highs will be in the mid 40s to low 50s, with lows in the low to mid 30s. The first frost is likely for Eastern Washington next week. (Add 3-5° to these temperatures for the Columbia Basin).

Stay tuned for more information as colder fall weather arrives in the Pacific Northwest.

Monday Storm: Strong Cold Front, Chance of Thunderstorms, and Heavy Rain

FastCast--Monday, Oct. 16 to Thursday, Oct. 19:

A potent and fast-moving storm system will move through Western Washington on Monday. The storm will begin with a strong cold front (with heavy rain at times) on Monday morning, during the commute. Then, from late morning to late evening, strong post-frontal showers will move through Western Washington, with a chance of thunderstorms across the region. A strong convergence zone will develop over Island, Skagit, and Whatcom Counties, and heavy showers will move through most of the lowlands in the afternoon. These showers will have heavy rain and gusty winds, with the potential for lightning, thunder, and small hail. Winds will pick up as well, gusting 25-35 mph in the lowlands and 35-45 mph in the North Sound, strongest on Whidbey Island. Rain totals will likely be in the 0.4-0.6" range in the lowlands, with some areas getting less, and areas under heavy showers getting more. Some showers will linger into Tuesday. Expect highs on Monday and Tuesday in the upper 50s to low 60s, with lows in the upper 40s to low 50s. On Wednesday, clouds will decrease, followed by sunny conditions on Thursday. With an atmospheric river to the north in BC, southerly flow will allow the lowlands to warm up significantly, with highs reaching the upper 60s to low 70s, with lows in the upper 40s to low 50s.

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A potent weather system is ahead for Western Washington on Monday, with the main impacts being rain (heavy at times), a chance of thunderstorms, and localized gusty winds. Let's take a look at the forecast!

Rain will come in 2 waves, with the initial cold front from 7-10 AM Monday, bringing heavy rain at times and locally windy conditions. Then, from 11 AM-7 PM, there is a region-wide chance of thunderstorms in heavy post-frontal showers moving onshore. Winds will be breezy (25-35 mph) in the lowlands and windy (35-45 mph) in the North Sound.

First, let's take a look at the European model forecast for rain through Monday night.

The European model shows most of the lowlands (except around Everett) getting 0.6-1" of rain, with up to 1.5" in Skagit County. Areas from Olympia south get 0.5-0.8", and the coast gets 1-1.5". The Olympics get up to 3", with 1-2" in the Cascades.

Let's compare this to the high-resolution NAM model, also showing rain through Monday night.

The NAM forecast shows less rain for the entirety of the lowlands, with 0.2-0.5" expected in this forecast. Areas from Mount Vernon northward get 0.5-0.75", with the coast picking up 0.6-1.2", and the Olympics & Cascades getting 2-4". 

Let's compare one more time to the HRRR high-resolution forecast, also through Monday night.

The HRRR sides more with the European than the NAM, showing 0.4-0.6" for the lowlands, but mainly south of Seattle. The HRRR shows a typical rain shadow NE of the Olympic Peninsula, but this will likely not happen on Monday due to Convergence Zone activity in that area. This forecast gives the coast 0.5-1", and gives the mountains 1-3".

Now, let's take a look at the thunderstorm potential on Monday. Thunderstorms are most likely in heavy post-frontal showers from late morning to late evening. Below is the NAM high-resolution forecast for CAPE (measure of instability in the atmosphere). More instability (CAPE) = higher chance of thunderstorms.

The NAM forecast below is for Monday afternoon.

The NAM shows high CAPE values of 250-1000 across the lowlands on Monday afternoon, highest from Seattle north to Vancouver BC.

Let's compare this to the HRRR high-resolution forecast, seen below (also for Monday afternoon).

The HRRR forecast shows CAPE values of 200-750 across the region, highest west of Olympia and from Port Townsend to Bellingham. 

Finally, let's take a look at the UW WRF forecast, also showing CAPE on Monday afternoon.

The UW WRF forecast agrees, showing CAPE values of 200-600 across Western Washington on Monday afternoon.

So...the bottom line is that lightning & thunder are possible in any shower from late Monday morning to Monday evening. Heavy rain, sudden drops in visibility, gusty winds, and small hail are also possible in any showers. Remember to go indoors if you hear thunder, and stay inside for at least 30 minutes.

We will end the blog with a look at the extended forecast, which has some interesting things to note. This is the Seattle forecast from the European EPS model.

Notice near-average highs on Monday & Tuesday, followed by significant warmth (low 70s possible) on Wednesday and Thursday. Then, from Friday to Monday, temperatures drop steadily. By next week, highs will likely struggle to get out of the mid 50s. Also, notice low temperatures drop to the low to mid 40s next week after remaining steady in the low 50s this week. We have a lot to watch in the extended forecast, so stay tuned!

2023 Annular Solar Eclipse Sky Cover Forecast

FastCast--Saturday, Oct. 14 to Wednesday, Oct. 18:

After warm days on Thursday and Friday, clouds and showers have returned to the Pacific Northwest. Continue reading the blog below for a sky cover forecast for the annular solar eclipse on Saturday morning. Expect a chance of showers on Saturday in the lowlands, most likely in the early morning and in the evening. Rain will be light, generally around 0.1". A break in the rain is likely on Sunday, with cloudy skies continuing. A stronger system will move through on Monday, with up to 0.75" of rain, winds gusting up to 30 mph, and some periods of heavy rain. Some showers will linger on Tuesday before rain leaves the area. Wednesday will begin cloudy but end mostly sunny. From Saturday to Tuesday, expect highs in the low 60s and lows in the upper 40s to low 50s. On Wednesday, expect highs increasing to the mid to upper 60s, with lows in the mid to upper 40s.

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On Saturday, an annular solar eclipse (known as a "ring of fire eclipse" due to how the moon obscures all but a ring of the sun) will move across the United States, with maximum totality beginning over the Central Oregon Coast and moving SE across the Desert Southwest, then over Texas, and exiting the US near Corpus Cristi on the Southern TX Gulf Coast. The eclipse will enter the US on the Oregon Coast around 9:13 AM PDT.

The map below from the Great American Eclipse website shows the eclipse's path and the path of totality.

Washington will be in the 70-80% totality area, with the highest levels of totality south of a line from Cape Flattery to Walla Walla. However, prospects of seeing the eclipse from Washington look grim.

Let's take a look at multiple sky cover forecasts, showing cloud cover around 9 AM.

The first forecast is the European model, seen below.

The European model shows most of Washington under complete cloud cover, with breaks in the clouds from Seattle to Bellingham and over most of the Columbia Basin (but not Yakima, Ellensburg, or areas south of the Tri Cities).

Let's compare this to the GFS forecast, seen below.

The GFS forecast shows a much cloudier picture. The only areas of partially clear skies are around the Tri Cities, near Ellensburg, and potentially near Port Townsend and Sequim, but all of those are only partially clear skies.

Next, let's take a look at the NAM high-resolution forecast.

The NAM shows the least cloudy forecast for Washington, with an area of mostly clear skies from Port Angeles to Bremerton to Tacoma and from Everett northward. In Eastern Washington, this forecast shows nearly clear skies from near Leavenworth to Clarkston.

Next, the HRRR high-resolution forecast.

The HRRR shows a cloudy forecast, with an odd narrow area of clear skies (with relatively low population) from near Mount Baker toward Pullman.

Finally, we'll end with the NOAA FV3 forecast, also showing cloud cover.

This forecast shows near total cloud cover in Western Washington, with some areas of partially clear skies north of Spokane, in parts of SE Washington, including near Clarkston, around the Tri Cities, and in extreme north-central Washington, north of the Methow Valley.

Overall, prospects for seeing the eclipse are very low in Western Washington and only somewhat better in Eastern Washington. The best resource to see cloud cover (besides looking outside) will be the UW Atmospheric Sciences Satellite Loop, which updates frequently and shows cloud cover over Washington.